1. Technical Field
The present invention generally relates to an apparatus and method for improving the dimensional quality of extruded food products. More specifically, the present invention relates to an apparatus and method that utilizes pre-expansion for improving the dimensional quality of extruded food products having complex shapes. In one aspect, the present invention relates to a method and apparatus to impart a distinct colored and/or flavored pattern into an extruded food product having superior dimensional aspects.
2. Description of the Related Art
The use of extrusion devices in the preparation of direct expanded food products is long practiced. Utilized to produce a variety of products such as ready-to-eat (R-T-E) cereals, snack foods and confections, extrusion remains prominent among food processes because of its versatility and efficiency.
Food processes utilizing extrusion devices typically include an edible substance such as dough which is introduced into a device and conveyed via a screw pump to an inlet where the substance is forced through an extruder die assembly. The extruder die assembly may perform a variety of functions: it may form or shape the extrudate; it may divide the extrudate into multiple extrudates; it may inject an additive substance into the extrudate; and it may compress and reduce the cross-sectional area of the extrudate.
Examples of devices used for extrusion of food products are illustrated in U.S. Pat. Nos. 2,858,217; 3,314,381; and 5,639,485. While extrusion dies have evolved over the years, the method by which an additive substance is supplied and injected into the extrudate has remained essentially unchanged.
For Example, in U.S. Pat. No. 2,858,217 to Benson, the introduction of coloring matter, such as a colored liquid dye, is accomplished via a series of apertures 40, 42, 44 disposed in the bridging strips 32, 34, 36 and supplied by horizontal passages 52, 54, 55 which are in fluid communication with the dye reservoir 46. The supplying of the liquid dye from the dye reservoir 46 to series of apertures 40, 42, 46 is by means of gravitational force. According to the Benson '217 device, dough material 18 is extruded through a divider block 22 which forces the dough material 18 to divide or spread around the bridging strips 32, 34, 36 so that voids 38 are formed into which the coloring matter is introduced via the series of apertures 40, 42, 44.
Similarly, in U.S. Pat. No. 3,314,381 to Fries et al., the fluid injection assembly is comprised of a hollow tubular injection member 29 in a helical spiral configuration, which includes a bore 37 through which pressurized injection fluid is supplied from a source 25 to a plurality of longitudinally spaced bores 39 into a distributing channel 38. The fluid along the length of channel 38 is injected into the passing dough as a substantially longitudinally continuous spiral band extending from substantially the central axis of the dough to either the outer face of the dough or a point short thereof. However, the Fries et al. '381 device is primarily adapted to relatively low pressure comestible extrusions.
U.S. Pat. No. 5,639,485 to Weinstein et al. and its related patents, disclose a method and apparatus for adding additives in flowing dough to make complexly patterned multicolored extrudates. The Weinstein et al. '485 invention and its progeny all disclose a high pressure extrusion device comprising an extruder die insert 20 which includes means for imparting at least one interstitial gap in the flowing dough by means of a plurality of dividing passageways (e.g., 44, 45, 46) formed by die dividing members 47. An additive (e.g., a food color or a second colored dough) may be injected via a plurality or array of evenly spaced food color injection ports 48 formed on the downstream side of die dividing member 47. The injection ports 48 are in fluid communication with a pressurized color supply 18 by means of supply ports 52, 54, 56 and supply passageway 50. The color fluid tends to fill the interstitial gaps in the flowing dough between passageways (e.g., 44, 45, 46) formed by and behind the die dividing members 47 to create a line in the shape of dividing members 47 in the extruded dough. The die insert 20 also includes notches 57 which are used to isolate the color fluid injected into the interstitial gap from spreading to the interior surface wall of die insert 20 thereby reducing if not eliminating the leakage of color fluid onto the outside of the extruded dough. Additionally, the die insert 20 can further include a means for sealing (e.g., “O” rings 60 and 62 as depicted) the color fluid supply reservoir 58 against premature admixture with dough.
The utilization of notches 57, sealing means 60, 62, and multiple enclosed injection ports 48 further complicates the design of the die insert making it harder to clean and maintain. Finally, injecting color fluid at discrete locations into downstream voids or interstitial gaps to disperse the fluid in a generally uniform manner requires precise control of flow rates, internal pressures, and viscosity of the extrudate and various additives. Furthermore, the design of each die insert 20 is limited to the physical constraints imposed by the previously mentioned design elements.
APV Baker, Inc., in an article presented at several Food Extrusion conferences in 1988, and partially authored by one of the inventors of the present application, discloses a technique for filling an extruded food product outside of a “double die” or in post extrudate operations. In the “double die” system, product expands out of one die opening into another die cavity where it is molded into a particular shape while it is still flexible. FIG. 6a is a perspective view of an embodiment of the prior art die assembly discussed in the APV Baker article. FIG. 6b is a side view of the prior art die assembly depicted in FIG. 6a. Referring to FIG. 6b, when the first die 605 is attached to the second die 665, the cylinder 615 fills a portion of the second die bore 665 and orifice 675 and extends out past the exit of the orifice 675. The orifice 675 and cylinder 615 form an annular open area at the exit of the orifice 675. As the individual ropes from the first die orifices 625 expand due to vapor flashing, the converging bore 665 of the second die restrains radial expansion and creates a hollow tube made up of multiple ropes as illustrated in FIG. 6c. A hollow cylinder 615 can be used to inject an additive substance into the hollow portion 682 of the tube. However, because the technique relates to an internal filling, it fails to disclose a way to impart a visibly distinct colored and/or flavored pattern into an extrudable food mass during extrusion. The APV Baker die assembly works best for co-extrusion of a cereal tube with a viscous creme or fruit filling. With co-extrusion, the nozzle 615 protrudes past the die face 675 so that the filling is being pumped into a low-pressure area 617. If the injection nozzle 615 stops short of the die face 675, then the filling injection has to overcome the higher pressure within the die cavity 665. Further, because the cylinder 615 extends out past the exit of the orifice 675, a rotating die face cutter cannot be used with the disclosed die assembly. Rather, a guillotine type cutter must be used, somewhere downstream of the cylinder 615 after the extruded food piece 680 has cooled and further solidified. Use of a guillotine type cutter following further solidification of an extruded food product results in a less clean, more fractured cut. What is needed is an extruder die assembly capable of mixing an additive substance at a variety of operating pressures which has improved seal characteristics and is simpler and easier to maintain.
Extruder die assemblies have also been used to apply a shape to a food product. FIG. 7a shows the exit face 752 of a potential forming die 750 used in a prior art extruder die assembly. Included within the periphery of the exit face 752 is a complexly shaped exit port 754. Upon exiting an extruder die assembly, the extruded mass is directly expanded (e.g., via flash puffing), both outwardly (transversely) in a radial direction, and longitudinally (axially) in the direction of flow. The flashed vapor is typically not captured and is thus vented to ambient air once the extruded mass has exited the die assembly. The extruded mass can then be cut into individual pieces using a rotating blade mechanism. The resulting individual pieces typically have a uniform, puffed shape with a cross-sectional shape that generally corresponds to the expanded outline of the die exit port. While the characteristics of the resulting individual pieces are satisfactory for simple geometric shapes (e.g., spheres, ovoids, and crescents), the design details of more complex shapes tend to be obscured or eliminated.
For example, the outline 756 of exit port 754 is designed to resemble a dog with two distinct legs, a neck, a body, a head, and a tail. When the forming die 750 is utilized in conjunction with a conventional direct expanded food process, the resulting product is a uniformly puffed food piece 780 as shown in FIG. 7b. While the shape of the outline 756 of exit port 754 is somewhat discernable in food piece 780, the design details of the two distinct legs, neck, and tail are generally diminished and obscured. The individual dimensional aspects of the two legs, neck, and tail are simply absorbed by the dimensional aspects of the body areas of the outline 756 of exit port 754 because, in part, of the radial expansion that occurs as the dough exits the die assembly.
One solution used to try to solve this problem was to simply further narrow the areas of the exit port where narrower aspects are desired in the food piece 780 in an effort to compensate the radial expansion. For example, the outline 756 of the exit port 754 could be further narrowed in the areas depicting the neck, leg, and tail. This option fails, however, because the driving force required through the narrow areas is much larger than the driving force required to force dough through the main body area. As a result, the extruded mass flows through the path of least resistance, which in FIG. 7a is the main body area of the dog. Substantially less extruded mass flows through the narrow areas.
One approach of imparting illustrations upon a food product is disclosed by U.S. Pat. No. 5,620,713 assigned to Pillsbury. The Pillsbury patent discloses a die set having an inner die and an outer die. The inner die is formed in a desired shape such as an animal or toy and the outer die has an annular opening surrounding the inner die. However, the outer shape of the food product is still determined by the outer die. The resultant dough dog must be sliced to observe the internal cross-sectional shaped animal or toy. In addition, at least two different doughs must be used. Further this technology requires cookie dough formulations, operates in a region of lower pressure and temperatures, and generates no flash-off expansion as the dough exits the die.
Similarly, U.S. Pat. No. 6,296,465, assigned to Nestec, discloses an extrusion die that produces a three-dimensional shape, having the general shape of a core surrounded by a ring. The core is extruded through a central outlet orifice and is surrounded by the ring extruded through an annular outlet orifice that surrounds the central outlet orifice. Prior to exiting the orifices, the extrudate first enters a convergent wall feed diaphragm, then it enters a divergent wall distribution chamber where it splits into two streams. From the divergent wall distribution chamber, the first stream enters the central duct by means of a circular central pre-expansion diaphragm. The second stream enters the conical convergent coaxial tubular extrusion duct by means of an annular pre-expansion member. The first stream eventually exits the central outlet orifice and the second stream eventually exits the annular outlet orifice. The resultant extruded product has the general shape of a core, surrounded by a ring, best illustrated by FIGS. 6a-6f of the Nestec Patent. The Nestec Patent, however, fails to disclose a method that provides desired outer narrow feature design details for extruded, complexly shaped food products. The Nestec Patent also does not utilize steam flash-off from the extrudate while contained within the walls of the second die, but rather relies upon steam vaporization and dough expansion that occurs at the exit of die nozzle 90. “Pre-expansion” as defined in the patent appears to refer to controlling the flow rate of dough prior to expansion.
Other prior art solutions, as disclosed in U.S. Pat. No. 5,304,055, issued to Nabisco (Nabisco I) and U.S. Pat. No. 5,435,714 also issued to Nabisco (Nabisco II) disclose an apparatus that utilizes a first cutting means to partially cut across the die orifice so that the extrudate rope is partially cut at an angle transverse to the direction of flow and then utilizes a second cutting means across the entire orifice to completely cut each of the partially cut extrudate ropes into individual pieces. The Nabisco patents relate only to the cutting apparatus to create three-dimensional shapes. In addition, the Nabisco Patents fail to solve the problem of diminished features due to expansion at the die, or reduced flow through narrow die areas. Further, the three-dimensional shapes that can be produced by introducing a single partial cut into a food extrudate are extremely limited.
Another extruder die assembly is illustrated in U.S. Pat. No. 3,054,677, assigned to The Quaker Oats Company, which discloses a method for making a dry, ready to eat cereal product by extruding a plurality of ropes or strands through a series of closely aligned orifices in a closed path configuration whereby the extruded strands expand to contact with each other and pass through a cutting device to form hollow, pillow shaped pieces. Prior to extrusion, a breaker plate is mounted behind a screen pack to increase the shearing action and further increase the backpressure. Because the expansion occurs in the open atmosphere after the extruding die, however, the flashed vapor is not captured and is thus vented to ambient air once the extruded mass has exited the die assembly. As a result, the dough strands do not adhere together as well as they would in an enclosure. Further, the '677 patent requires a separate rotary cutting device away from the die assembly which requires more equipment and floor space. In addition, the rotary cutting device disclosed in the '677 patent limits the shapes of the resultant food products to crimped, pillow-like shapes. What is needed is a die assembly that can enable a rotating die face cutter to cut multiple stranded, adhered, and extruded dough products.
Consequently, a need exists for an improved apparatus and method for enhancing the quality of dimensional design aspects of extruded, complexly shaped food products. The improved method and apparatus should permit novel symmetrical and asymmetrical shapes to be produced. In one embodiment, it should permit pre-expanded extruded dough of various geometries to be formed into a desired shape having a desired texture and then cut by a rotating die face cutter. In one embodiment, it should permit production of extruded food pieces having substantially non-rounded edges. Further, the improved apparatus and method should, in one embodiment, provide a means to add color and/or flavor to the extruded, complexly shaped food products.